The ecological disposal of domestic waste and the production of useful products, specifically combustion gases from it, form the subject matter of a number of proposals in the prior art.
Domestic waste is usually treated after having been accumulated as municipal waste. Its composition is highly variable. It is often referred to as “biomass”, since it contains a considerable proportion of food residues, but in reality it is only partially a biomass. It may, and frequently does, also contain considerable amounts of cardboard and paper and generally cellulosic material or partly cellulosic material such as wood. It also does contain inorganic materials, such as metal or glass or even rocks or sand, and other materials such as plastics, fabrics, and so on. As a result, part of the waste can produce combustible gases and an oxidation residue and part remains substantially unchanged, so that, at the end of any disposal and utilization process, a substantially inorganic ash is produced. All possible compositions of domestic waste can be treated by the method and apparatus of this invention, which is therefore not limited to any range of compositions and the term “domestic waste” is intended herein to include all compositions, but of course the parameters of the process must be controlled to take into consideration the composition being treated. This, however, comes within the capabilities of skilled persons and requires no particular description, although some indication will be given later.
EP-A 136 277 A2 discloses an apparatus and method for gasifying what is called “biomass fuels”. A mass refractory layer has a first inclined fuel supporting ramp. A mass of refractory is provided opposing surface to define a primary gasification chamber. The chamber is sealed by another mass of refractory. Biomass fluid, heated by radiation from the refractory, carbonizes and releases volatile gases. Additionally, the apparatus comprises a lower refractory layer having a second inclined ramp, which has a plurality of inlet holes to provide air distribution in a specific combustion zone located below the zone in which carbonization occurs.
WO 96/00267 discloses a process in which waste is charged into a reactor, an oxygen-containing gas is injected into it, solid products and gaseous products produced by the treatment are withdrawn, and the treatment results from the successive passage of the waste through a heating and drying zone, a thermolysis zone, an oxidation zone and a cooling zone. In this application the control of the temperature to maintain it between 700 and 1400° C. is effected by controlling at least one of the parameters among the oxygen mass fraction and the mass fractions of the incombustible and the combustible components of the waste.
WO 99/37738 (some of the inventors thereof are the same as those of the preceding application) discloses a method of processing municipal wastes, primarily highly humid ones, which comprises drying, pyrolyzing and gasifying the waste by means of an oxygen-containing gas, at temperatures between 800 and 1300° C., by controlling the same parameters as are controlled in WO 96/00267, with the feature that the smoke gas, preferably a mixture with air, is used as the gasifying agent and the mass fractions of oxygen in said agent and of incombustible and combustible components in the waste satisfy a certain quantitative condition.
WO 99/42540 discloses a process for the gasification of biomass or biomass-comprising materials, which gasification takes place in a reverse-flow reactor in which the line of direction in which gas is passed through the biomass cuts the line of direction in which the biomass is supplied.
Japanese Application No. 07324432 discloses a burner for municipal refuse, wherein the temperature of the burning space of the burner chamber is raised to about 2000° C., then air is supplied and the temperature of the uppermost layer of a fuel packed bed is raised.
Japanese Application No. 10153892 discloses a gasification furnace for municipal waste divided by a partition plate into a first-stage gasification chamber for pre-heating and drying and a second-stage gasification chamber for obtaining partly oxidized gas.
The aforesaid and other prior art patents are not satisfactory for an efficient treatment of municipal wastes, for various reasons. Some of them do not permit continuous operation, or, if they permit it, it is very difficult to control it. The efficiency of their processes is limited. The structure and the operation of the reactors are complicated and expensive. Gas leakage problems are not considered, or if considered, are not adequately solved. The waste must be sorted according to composition and dimensions of particles before recycling.
This invention therefore has the purpose of providing a method and apparatus for the disposal of domestic wastes and the production of fuel gas from it that are free of the defects of the prior art methods and apparatus.
Another purpose of the invention is to provide such a method and apparatus that are adapted to continuous production.
A further purpose is to provide such method and apparatus that permit control of the feed of waste and of the rate of production in a full and adequate manner.
A still further purpose is to provide such a method and apparatus that are reliable in operation.
A still further purpose is to provide such a method and apparatus that are simple and economically convenient.
A still further purpose is to provide such a method and apparatus that prepares insert and metal materials for use.
Other purposes and advantages of the invention will appear as the description proceeds.